Device for detecting leakage of liquid in tank

Abstract

A device placed in a tank and used for detecting a leakage of liquid in the tank. Vertical measurement tube passages ( 10, 14 ) into which the liquid in the tank is introduced have a measurement tube ( 10 ) and a measurement thin tube ( 14 ). The measurement thin tube ( 14 ) communicates with the measurement tube and is located lower than the measurement tube. The measurement thin tube has a cross-sectional area that is equal to or smaller than {fraction (1/50)} of that of the measurement tube. A thermal flow sensor ( 16 ) used for measuring a liquid flow rate is attached to the measurement thin tube ( 14 ). There is provided leakage detecting means ( 22 ) for detecting a leakage of liquid in the tank according to the flow rate value measured by the sensor. The leakage detecting means generates a leakage detection signal when a flow rate value measured by the sensor is within a range greater than 0 and smaller than the flow rate value obtained when liquid is added to the tank or when the liquid in the tank is taken out. Thus, even a leakage of a very small amount is detected easily and accurately without stopping the use of the tank.

1. A device for detecting leakage of liquid in a tank, which is inserted into the tank to detect the leakage of liquid in the tank, comprising:
 a measurement tube passage into which the liquid in the tank is-introduced, the measurement tube passage including a measurement tube and a measurement thin tube communicating with the measurement tube and positioned below the measurement tube and having a cross-sectional area smaller than that of the measurement tube;  
 a sensor for use in measuring a flow rate of the liquid in the measurement thin tube, the sensor being attached to the measurement thin tube; and  
 leakage detection means for detecting the leakage of the liquid in the tank based on the flow rate measured using the sensor.  
 
   
   
     2. The device for detecting the leakage of liquid in the tank according to  claim 1 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/50)} or less of that of the measurement tube. 
   
   
     3. The device for detecting the leakage of liquid in the tank according to  claim 1 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/100)} or less of that of the measurement tube. 
   
   
     4. The device for detecting the leakage of liquid in the tank according to  claim 1 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/300)} or less of that of the measurement tube. 
   
   
     5. The device for detecting the leakage of liquid in the tank according to  claim 1 , wherein the measurement tube and the measurement thin tube are directed substantially in a vertical direction. 
   
   
     6. The device for detecting the leakage of liquid in the tank according to  claim 1 , wherein the sensor is a thermal flow rate sensor. 
   
   
     7. The device for detecting the leakage of liquid in the tank according to  claim 6 , wherein the thermal flow rate sensor includes a flow rate detection section and a temperature detection section, and the leakage detection means obtains the flow rate subjected to temperature compensation by an electric circuit comprising the flow rate detection section and the temperature detection section. 
   
   
     8. The device for detecting the leakage of liquid in the tank according to  claim 7 , wherein either of the flow rate detection section and the temperature detection section comprises a heat transfer member which contacts the outer surface of the measurement thin tube. 
   
   
     9. The device for detecting the leakage of liquid in the tank according to  claim 1 , wherein the leakage detection means emits a leakage detection signal, when the flow rate measured using the sensor is in a range greater than 0 and smaller than a flow rate value obtained during liquid replenishment into the tank or liquid pumping-out from the tank. 
   
   
     10. The device for detecting the leakage of liquid in the tank according to  claim 1 , wherein the measurement tube passage is formed through a sheath tube and a sensor holder member attached to a lower part of the sheath tube, the sensor holder member holds the sensor, and the measurement thin tube is disposed through the sensor holder member. 
   
   
     11. The device for detecting the leakage of liquid in the tank according to  claim 10 , wherein a cap member is attached to an upper part of the sheath tube, and the cap member is provided with a communication path for allowing the measurement tube to communicate with the outside and means for fixing the device to an opening of the tank. 
   
   
     12. A device for detecting leakage of liquid in a tank, which is inserted into the tank to detect the leakage of liquid in the tank, comprising:
 a measurement tube passage into which the liquid in the tank is introduced, the measurement tube passage including a measurement tube and a measurement thin tube communicating with the measurement tube and positioned below the measurement tube and having a cross-sectional area smaller than that of the measurement tube;  
 a sensor for use in measuring a flow rate of the liquid in the measurement thin tube, the sensor being attached to the measurement thin tube;  
 liquid level detection means for use in detecting a height of a surface of the liquid; and  
 leakage detection means for detecting the leakage of the liquid in the tank based on a corrected flow rate obtained by correcting the flow rate measured using the sensor based on a liquid level detected using the liquid level detection means and a value of a parameter concerning the shape of the tank.  
 
   
   
     13. The device for detecting the leakage of liquid in the tank according to  claim 12 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/50)} or less of that of the measurement tube. 
   
   
     14. The device for detecting the leakage of liquid in the tank according to  claim 12 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/100)} or less of that of the measurement tube. 
   
   
     15. The device for detecting the leakage of liquid in the tank according to  claim 12 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/300)} or less of that of the measurement tube. 
   
   
     16. The device for detecting the leakage of liquid in the tank according to  claim 12 , wherein the measurement tube and the measurement thin tube are directed substantially in a vertical direction. 
   
   
     17. The device for detecting the leakage of liquid in the tank according to  claim 12 , wherein the sensor is a thermal flow rate sensor. 
   
   
     18. The device for detecting the leakage of liquid in the tank according to  claim 17 , wherein the thermal flow rate sensor comprises a flow rate detection section and a temperature detection section, and the leakage detection means obtains the flow rate subjected to temperature compensation by an electric circuit comprising the flow rate detection section and the temperature detection section. 
   
   
     19. The device for detecting the leakage of liquid in the tank according to  claim 18 , wherein either of the flow rate detection section and the temperature detection section comprises a heat transfer member which contacts the outer surface of the measurement thin tube. 
   
   
     20. The device for detecting the leakage of liquid in the tank according to  claim 12 , wherein the liquid level detection means is a pressure sensor which detects a liquid pressure received from the liquid in the tank. 
   
   
     21. The device for detecting the leakage of liquid in the tank according to  claim 12 , wherein the parameter concerning the shape of the tank is a ratio of an effective cross-sectional area of the tank with respect to the cross-sectional area of the measurement tube in an equal height, and the corrected flow rate is obtained by multiplying the flow rate by the value of the parameter in the liquid level. 
   
   
     22. The device for detecting the leakage of liquid in the tank according to  claim 12 , wherein the leakage detection means emits a leakage detection signal, when the corrected flow rate is in a range greater than 0 and smaller than a corrected flow rate value obtained during liquid replenishment into the tank or liquid pumping-out from the tank. 
   
   
     23. The device for detecting the leakage of liquid in the tank according to  claim 12 , wherein the measurement tube passage is formed through a sheath tube and a sensor holder member attached to a lower part of the sheath tube, the sensor holder member holds the sensor and the liquid level detection means, and the measurement thin tube is disposed through the sensor holder member. 
   
   
     24. The device for detecting the leakage of liquid in the tank according to  claim 23 , wherein a cap member is attached to an upper part of the sheath tube, and the cap member is provided with a communication path for allowing the measurement tube to communicate with the outside and means for fixing the device to an opening of the tank. 
   
   
     25. A device for detecting leakage of liquid in a tank, which is inserted into the tank to detect the leakage of liquid in the tank, comprising:
 a measurement tube passage into which the liquid in the tank is introduced, the measurement tube passage including a measurement tube and a measurement thin tube communicating with the measurement tube and positioned below the measurement tube and having a cross-sectional area smaller than that of the measurement tube;  
 a sensor for use in measuring a flow rate of the liquid in the measurement thin tube, the sensor being attached to the measurement thin tube;  
 an open/close valve provided in an upper part of the measurement tube; and  
 leakage detection means for detecting the leakage of the liquid in the tank based on an integrated value of the flow rate measured using the sensor after closing the open/close valve for a predetermined time and subsequently opening the valve.  
 
   
   
     26. The device for detecting the leakage of liquid in the tank according to  claim 25 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/50)} or less of that of the measurement tube. 
   
   
     27. The device for detecting the leakage of liquid in the tank according to  claim 25 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/100)} or less of that of the measurement tube. 
   
   
     28. The device for detecting the leakage of liquid in the tank according to  claim 25 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/300)} or less of that of the measurement tube. 
   
   
     29. The device for detecting the leakage of liquid in the tank according to  claim 25 , wherein the measurement tube and the measurement thin tube are directed substantially in a vertical direction. 
   
   
     30. The device for detecting the leakage of liquid in the tank according to  claim 25 , wherein the sensor is a thermal flow rate sensor. 
   
   
     31. The device for detecting the leakage of liquid in the tank according to  claim 30 , wherein the thermal flow rate sensor includes a flow rate detection section and a temperature detection section, and the leakage detection means obtains the flow rate subjected to temperature compensation by an electric circuit comprising the flow rate detection section and the temperature detection section. 
   
   
     32. The device for detecting the leakage of liquid in the tank according to  claim 31 , wherein either of the flow rate detection section and the temperature detection section comprises a heat transfer member which contacts the outer surface of the measurement thin tube. 
   
   
     33. The device for detecting the leakage of liquid in the tank according to  claim 25 , wherein the leakage detection means controls opening/closing of the open/close valve. 
   
   
     34. The device for detecting the leakage of liquid in the tank according to  claim 25 , further comprising liquid level detection means for use in detecting a height of a surface of the liquid, wherein the leakage detection means corrects an integrated value of the flow rate measured using the sensor based on a liquid level detected by the liquid level detection means and a value of a parameter concerning the shape of the tank to obtain a corrected integrated value, and detects the leakage of the liquid in the tank based on the corrected integrated value. 
   
   
     35. The device for detecting the leakage of liquid in the tank according to  claim 34 , wherein the liquid level detection means is a pressure sensor which detects a liquid pressure received from the liquid in the tank. 
   
   
     36. The device for detecting the leakage of liquid in the tank according to  claim 34 , wherein the parameter concerning the shape of the tank is a ratio of an effective cross-sectional area of the tank with respect to the cross-sectional area of the measurement tube in an equal height, and the corrected integrated value is obtained by multiplying the integrated value by the value of the parameter in the liquid level. 
   
   
     37. The device for detecting the leakage of liquid in the tank according to  claim 25 , wherein the leakage detection means emits a leakage detection signal, when the integrated value of the flow rate or the corrected integrated value is not less than a predetermined value. 
   
   
     38. The device for detecting the leakage of liquid in the tank according to  claim 25 , wherein the measurement tube passage is formed through a sheath tube and a sensor holder member attached to a lower part of the sheath tube, the sensor holder member holds the sensor, and the measurement thin tube is disposed through the sensor holder member. 
   
   
     39. The device for detecting the leakage of liquid in the tank according to  claim 38 , wherein a cap member is attached to an upper part of the sheath tube, the cap member is provided with a communication path for allowing the measurement tube to communicate with the outside and means for fixing the device to an opening of the tank, and the open/close valve is disposed on the communication path. 
   
   
     40. A device for detecting leakage of liquid in a tank, which is inserted into the tank to detect the leakage of liquid in the tank, comprising:
 a measurement tube passage into which the liquid in the tank is introduced, the measurement tube passage including a measurement tube and a measurement thin tube communicating with the measurement tube and positioned below the measurement tube and having a cross-sectional area smaller than that of the measurement tube;  
 a first sensor for use in measuring a flow rate of the liquid in the measurement thin tube, the first sensor being attached to the measurement thin tube;  
 a second sensor for use in detecting a direction of a flow of the liquid in the measurement thin tube, the second sensor being attached to the measurement thin tube; and  
 leakage detection means for detecting the leakage of the liquid in the tank based on a combination of the direction of the flow of the fluid detected using the second sensor and the flow rate measured using the first sensor.  
 
   
   
     41. The device for detecting the leakage of liquid in the tank according to  claim 40 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/50)} or less of that of the measurement tube. 
   
   
     42. The device for detecting the leakage of liquid in the tank according to  claim 40 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/100)} or less of that of the measurement tube. 
   
   
     43. The device for detecting the leakage of liquid in the tank according to  claim 40 , wherein the cross-sectional area of the measurement thin tube is {fraction (1/300)} or less of that of the measurement tube. 
   
   
     44. The device for detecting the leakage of liquid in the tank according to  claim 40 , wherein the measurement tube and the measurement thin tube are directed substantially in a vertical direction. 
   
   
     45. The device for detecting the leakage of liquid in the tank according to  claim 40 , wherein the first sensor is a thermal flow rate sensor. 
   
   
     46. The device for detecting the leakage of liquid in the tank according to  claim 45 , wherein the thermal flow rate sensor includes a flow rate detection section and a temperature detection section, and the leakage detection means obtains the flow rate subjected to temperature compensation by an electric circuit comprising the flow rate detection section and the temperature detection section. 
   
   
     47. The device for detecting the leakage of liquid in the tank according to  claim 46 , wherein either of the flow rate detection section and the temperature detection section comprises a heat transfer member which contacts the outer surface of the measurement thin tube. 
   
   
     48. The device for detecting the leakage of liquid in the tank according to  claim 46 , wherein the second sensor comprises a pair of thermometric sensors disposed above and below the flow rate detection section of the thermal flow rate sensor. 
   
   
     49. The device for detecting the leakage of liquid in the tank according to  claim 48 , wherein either of the pair of thermometric sensors comprises a heat transfer member which contacts the outer surface of the measurement thin tube. 
   
   
     50. The device for detecting the leakage of liquid in the tank according to  claim 40 , wherein the leakage detection means emits a leakage detection signal, when the direction of the flow of the liquid detected using the second sensor is a downward direction and the flow rate measured using the first sensor is in a predetermined range. 
   
   
     51. The device for detecting the leakage of liquid in the tank according to  claim 50 , wherein the leakage detection means emits the leakage detection signal in a case where the direction of the flow of the liquid detected using the second sensor is a downward direction and a duration of time within which the flow rate measured using the first sensor is in a predetermined range is not less than a predetermined ratio within a predetermined time. 
   
   
     52. The device for detecting the leakage of liquid in the tank according to  claim 40 , wherein the measurement tube passage is formed through a sheath tube and a sensor holder member attached to a lower part of the sheath tube, the sensor holder member holds the first and second sensors, and the measurement thin tube is disposed through the sensor holder member. 
   
   
     53. The device for detecting the leakage of liquid in the tank according to  claim 52 , wherein a cap member is attached to an upper part of the sheath tube, and the cap member is provided with a communication path for allowing the measurement tube to communicate with the outside and means for fixing the device to an opening of the tank.